System and Method for Intravascular Structural Analysis Compensation of Chemical Analysis Modality

ABSTRACT

A multimodal intravascular analysis uses a structural intravascular analysis modality to compensate for a chemical analysis modality. Examples of structural analysis are IVUS, OCT, including optical coherence domain Reflectometry (OCDR) and optical frequency domain imaging (OFDI), and/or sonar rangefinding. Examples of chemical or functional analysis are optical, NIR, Raman, fluorescence and spectroscopy, thermography and reflectometry. In one example, the structural analysis is used to characterize the environment structurally, such as catheter head-vessel wall distance. This information is then used to select from two or more algorithms which are depth specific (e.g. shallow vs. deep), to achieve improved accuracy in the chemical or functional analysis.

This application claims the benefit under 35 U.S.C. §120 of the filingdate of non-provisional patent application Ser. No. 12/062,188 filedApr. 3, 2008, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

Intravascular ultrasound (IVUS) is a medical imaging technology. It usesa specially designed catheter that includes an ultrasound transducer. Inthe typical application, the catheter is inserted into the vascularsystem of a patient and moved to an artery or vein of interest. Itallows the doctor to obtain an image of the inner walls of the bloodvessels, even through intervening blood. Specifically, it allowsvisualization of the endothelium (inner wall) of blood vessels, andstructures within the vessels walls.

In its typical application, IVUS is used in coronary arteries of theheart to locate, identify and characterize atherosclerotic plaques inpatients. It can be used both to determine the plaque volume in theblood vessel wall and also the degree of stenosis (narrowing) of theblood vessels. In this way, IVUS is an important technology for thestructural analysis of blood vessels.

Optical coherence tomography (OCT) is an emerging technology that alsoprovides structural information similar to IVUS. OCT also uses acatheter that is moved through the blood vessels to regions of interest.An optical signal is emitted from the catheter head and the returningsignal is analyzed for phase or coherence in a Michelson interferometer,usually.

OCT has potential advantages over IVUS. Generally, OCT provides theopportunity for much higher spatial resolution, but the optical signalshave limited penetration through blood and attenuate very quickly whenpropagating through the walls of the blood vessels.

An objective to using systems based on OCT and IVUS structural imagingtechnologies is the early identification of vulnerable plaques sincedisruption or rupture of atherosclerotic plaques appears to be the majorcause of heart attacks and strokes. After the plaques rupture, localobstructive thromboses form within the blood vessels. Both venous andarterial thrombosis can occur. A coronary thrombus often initially formsat the site of rupture of a vulnerable plaque; i.e. at the location of aplaque with a lipid-rich core and a thin fibrous cap (thin-capfibroatheroma or TCFA).

Another class of intravascular analysis systems directed to thediagnosis and analysis of atherosclerosis uses chemical analysismodalities. These approaches generally rely on optical analysisincluding near infrared (NIR), Raman, and fluorescence spectralanalysis.

Probably the most common and well developed of these chemical analysismodalities is NIR analysis of the blood vessel walls. Similar to OCT,NIR analysis utilizes an intravascular optical catheter. In a typicalapplication, the catheter is driven by a pullback and rotation unit thatsimultaneously rotates the catheter head around its longitudinal axiswhile withdrawing the catheter head through the region of the bloodvessel of interest.

During this pullback operation, the spectral response of the innervessel walls is acquired in a raster scan operation. This provides aspatially-resolved spectroscopic analysis of the region of interest. Thestrategy is that by determining the spectroscopic response of bloodvessel walls, the chemical constituents of those blood vessel walls canbe determined by application of chemometric analysis for example. Inthis way, potentially vulnerable plaques are identified so that, forexample, stents can be deployed in order reduce the risk of myocardialinfarction.

In Raman spectral analysis, the inner walls of the blood vessel areilluminated by a narrow band, such as laser, signal. The Raman spectralresponse is then detected. This response is generated by the inelasticcollisions betweens photons and the chemical constituents in the bloodvessel walls. This similarly produces chemical information for thevessel walls.

Problems associated with Raman analysis are, however, that the Ramanprocess is a very weak and requires the use of high power opticalsignals in order to generate an adequate Raman response. Fluorescencehas some advantages in that the fluorescence response is sometimes muchlarger than the Raman response. Generally, however, fluorescenceanalysis does not yield as much information as Raman or NIR analysis.

Another advantage of NIR analysis is that the blood flow does notnecessarily have to be occluded during the analysis. The judiciousselection of the wavelengths of the optical signals allows adequatepenetration through intervening blood to the vessels walls and back tothe catheter head.

In an effort to obtain the valuable information from both the chemicaland structural analysis modalities, hybrid IVUS/optical catheters havebeen proposed. For example, in U.S. Pat. No. 6,949,072, a “device forvulnerable plaque detection” is disclosed. Specifically, this patent isdirected to intravascular probe that includes optical waveguides andports for the near infrared analysis of the blood vessel walls whilesimultaneously including an ultrasound transducer in the probe in orderto enable IVUS analysis of the blood vessel walls.

SUMMARY OF THE INVENTION

The present invention concerns multimodal intravascular analysis. Ituses a structural intravascular analysis modality to compensate for achemical analysis modality. Examples of structural analysis are IVUS,OCT, including optical coherence domain Reflectometry (OCDR) and opticalfrequency domain imaging (OFDI), and/or sonar rangefinding. Examples ofchemical or functional analysis are optical, NIR, Raman, fluorescenceand spectroscopy, thermography and reflectometry. In one example, thestructural analysis is used to characterize the environment, such ascatheter head-vessel wall distance. This information is then used toselect from two or more algorithms that are depth specific (e.g. shallowvs. deep), to achieve improved accuracy in the chemical or functionalanalysis.

In general, according to one aspect, the invention features a method foranalyzing blood vessel walls. This method comprises advancing a catheterthrough blood vessels to regions of interest of blood vessel walls. Afirst form of energy is transmitted from the head of the catheter anddetected after interaction with the blood vessel walls. A second form ofenergy is also transmitted and detected from the blood vessel walls. Thefirst form of energy is used to determine a structural measureassociated with the blood vessel walls. Then the blood vessel walls areanalyzed using the second form of energy compensated by the determinedstructural measure based on the detected first form of energy.

In this way, the present invention is directed to a hybrid system thatcombines the use of two different analysis modalities: a first modalityassociated with a more structural analysis; combined with a secondmodality that is largely a chemical analysis modality. In this way, thestructural analysis information is used to compensate or improve theinformation from the chemical analysis, which has the potential ofproviding better direct information concerning the regions of interestand whether a specific vulnerable plaque lesion is present, or not.

In one embodiment, the first form of energy is ultrasonic energy. Inthis way, the system has an IVUS capability. In some examples, thisultrasound signal is generated photo acoustically. In other examples,the ultrasonic energy is used in a simpler sonar rangefindingimplementation. In still other examples, the first form of energy is anoptical signal as used in OCT analysis.

In the preferred embodiment, the second form of energy is opticalenergy. Specifically, analyzing the blood vessel walls comprises usingthe detected optical energy to resolve the spectral response of theblood vessel walls. In examples, the NIR, fluorescence or Raman responseof the blood vessels walls is obtained.

In still further examples, simply the reflectances of the blood vesselwalls are detected using the second form of energy.

In one example, the first form of energy is used to select a predictionmodel for analyzing the detected second form of energy.

In other examples, the first form of energy is used to select thresholdsfor analyzing the detected second form of energy.

In implementations, the structural measure includes a physicalrelationship between the head of the catheter and the blood vesselwalls. In other cases, it includes the thickness of a plaque of theblood vessel walls or the thickness of the blood vessel wallsthemselves. In this way, by determining the distance between thecatheter head and the blood vessel walls using the structural analysismodality on a point-by-point basis, the chemometric analysis generatedby the NIR analysis of the blood vessel walls can be compensated withthis information to thereby improve the accuracy of this chemometricanalysis.

Depending on the various implementations, the first form of energy andthe second form of energy are transmitted simultaneously whilewithdrawing the catheter head through the blood vessels. In otherexamples, the first form of energy and the second form of energy aregenerated and detected during successive of pullback and rotationoperations of the catheter head.

In general, according to another aspect, the invention features a systemfor analyzing blood vessel walls. This system comprises a catheter thatis advanced through blood vessels to regions of interest of the bloodvessel walls. The catheter comprises a catheter head. It houses a firstenergy form system that transmits a first form of energy from the headof the catheter and detects the first form of energy from the bloodvessel walls and a second energy form system that transits a second formof energy from the catheter and receives the second form of energy fromthe blood vessel walls. A pullback and rotation system is used tosimultaneously withdraw the catheter head through the blood vesselswhile rotating the head around a longitudinal axis. Finally, an analyzercombines the information from each of the first and second form analysesin order to improve the analysis of the blood vessel walls.Specifically, the analyzer determines a structural measure using thefirst form of energy and then analyzes the blood vessel walls using thedetected second form of energy after compensation by the determinedstructural measure.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is a cross-sectional view of an intravascular probe with aguidewire in a distal end of a catheter;

FIG. 2 is a schematic diagram illustrating the use of the cathetersystem and a system controller, according to the invention;

FIG. 3 is a flow diagram illustrating a method for using informationfrom a structural analysis modality to compensate information from achemical analysis modality, according to the invention;

FIG. 4 is a flow diagram illustrating another method for usinginformation from a structural analysis modality to compensateinformation from a chemical analysis modality, according to theinvention; and

FIG. 5 is a schematic diagram illustrating the point by point method forchemometric model compensation according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of an intravascular catheter system 100 thatcombines two analysis modalities based on two forms of energy: a firstform of energy that yields spatially resolved structural information oreven an image and a second form of energy that yields spatially resolvedchemical information. Information from both sources is used to identifyvulnerable plaques 102 in an arterial wall 104 of a patient. Thecombination of both: 1) chemical analysis modalities, using infraredspectroscopy to detect lipid content, and 2) morphometric analysismodalities, using IVUS to detect cap thickness or distance to vesselwall, enables greater selectivity in identifying potentially vulnerableplaques than either detection modality alone. These two detectionmodalities can achieve high sensitivity even in an environmentcontaining blood.

In more detail, the intravascular catheter system 100 includes aguidewire lumen 110 at a distal end of the catheter system 100. Intypical operation, the intravascular catheter 100 is advanced into ablood vessel 18 using guidewire 108 that is threaded through theguidewire lumen 110.

The catheter system 100 further comprises an inner scanning catheterhead 112 and a sheath 114. The combination of the scanning catheter head112 and sheath 114 enables the inner scanning catheter head 112 toperform longitudinal translation and rotation while the sheath 114prevents this movement from damaging the vessel 18 and specificallywalls 104.

At least the distal end of the sheath 114 is composed of materials thatare transparent to infrared light (e.g., a polymer). The head of thescanning catheter 112 is located at the distal end of the catheter 100and includes an optical bench 118 to transmit and receive infrared lightand an ultrasound transducer 120 to transmit and receive ultrasoundenergy.

The optical bench 118 contains the terminations of a delivery fiber 122and a collection fiber 123, which extend between the proximal and distalends of the catheter 100. A light source couples light into a proximalend of the delivery fiber 122, and a delivery mirror 124 redirects light125 emitted from a distal end of the delivery fiber 122 towards thearterial wall 104. A collection mirror 126 redirects light 127 scatteredfrom various depths of the arterial wall 104 into a distal end of thecollection fiber 123.

The ultrasound transducer system 120, which is longitudinally adjacentto the optical bench 118, includes one or more transducers that directultrasound energy 130 towards the arterial wall 104 and receiveultrasound energy 132 reflected from the arterial wall 104. Using timemultiplexing in one implementation, a single ultrasound transducer bothgenerates the transmitted energy 130 and transduces received energy 132into an electrical signal carried on wires 128. For example, during afirst time interval, an electrical signal carried on wires 128 actuatesthe ultrasound transducer 120 to emit a corresponding ultrasound signal130. Then during a second time interval, after the ultrasound signal 130has reflected from the arterial wall 104, the ultrasound transducer 120produces an electrical signal carried on wires 128. This electricalsignal corresponds to the received ultrasound signal 132. The receivedelectrical signal 132 is used to reconstruct the shape of the arterialwall, including cap thickness t_(c) of any plaque 102 and/or a distanceD(wall) between the head or distal end of the scanning catheter 112 andthe vessel wall 104, for example, for each spatially resolved pointalong the wall 104 as the head is scanned through the vessel 18.

In other embodiments, the ultrasound signal is generatedphoto-acoustically by sending a light pulse through optical fiber withenough energy to create an acoustic event that is detected by the IVUStransducer system 120.

Inside the sheath 114 is a transmission medium 134, such as saline orother fluid, surrounding the ultrasound transducer 120 for improvedacoustic transmission. The transmission medium 134 is also selected tobe transparent to the infrared light emitted from and received by theoptical bench 118.

A torque cable 136 is attached to a scanning catheter housing 116 andsurrounds the optical fibers 122, 123 and the wires 128. This cable 136transmits the torque from a pullback and rotation system through to thescanning catheter head 112. This feature enables the scanning catheterhead 112 to rotate within sheath 114 to circumferentially scan thearterial wall 104 with light 125 and ultrasound energy 130.

FIG. 2 illustrates an exemplary system for detecting and analyzing thespectral responses in two energy-form scanning.

The system generally comprises the catheter 100, a controller 300, and auser interface 320.

In operation, first the guide wire and then the catheter 100 areinserted into the patient 2 via a peripheral vessel, such as the femoralartery 10. The catheter head 112 is then moved to a desired targetregion, such as a coronary artery 18 of the heart 16 or the carotidartery 14. This is achieved by moving the catheter head 112 up throughthe aorta 12, riding on the guidewire.

When at the desired site, NIR radiation is generated, in one embodiment.In preferred embodiment, a tunable laser in the chemical analysissubsystem 312 generates a narrowband optical signal that is wavelengthscanned over a scan band in the NIR, covering one or more spectral bandsof interest. In other embodiments, one or more broadband sources areused to access the spectral bands of interest. In either case, theoptical signals are coupled into the single mode delivery fiber 122 ofthe catheter 100 to be transmitted to the optical bench 118.

In other examples, reflectances are measured. This is based on thediscovery that lipid-rich plaques are “brighter” than other plaques, andblood is typically “darker” than tissue in the NIR. So, just abrightness measurement, corrected for blood depth, sometimes yieldsadequate accuracy for detection.

In the current embodiment, optical radiation in the near infrared (NIR)spectral regions is used for spectroscopy. Exemplary scan bands include1000 to 1450 nanometers (nm) generally, or 1000 nm to 1350 nm, 1150 nmto 1250 nm, 1175 nm to 1280 nm, and 1190 nm to 1250 nm, morespecifically. Other exemplary scan bands include 1660 nm to 1740 nm, and1630 nm to 1800 nm.

However, in other optical implementations, broad band signals, otherscan bands, or single frequency excitation signals appropriate forfluorescence and/or Raman spectroscopy are generated by the chemicalanalysis subsystem 312. In still other implementations, scan bands inthe visible or ultraviolet regions are used.

In the current embodiment, the returning light is transmitted back downmultimode collection fiber 123 of the catheter 100. The returningradiation is provided to the chemical analysis subsystem 312, which cancomprise one or multiple optical detectors or spectrometers.

The chemical analysis subsystem 312 monitors the response of thedetector, while controlling the source or tunable laser in order toresolve the spectral response of vessel walls 104 including a targetarea, typically on an inner wall of a blood vessel 18 and through theintervening blood or other unwanted signal sources. This spectralresponse is further spatially resolved as the catheter head is rotatedand pulled back through the vessel 18.

As a result, the chemical analysis subsystem 312 is able to collectspectra. When the acquisition of the spectra is complete, chemicalanalysis subsystem 312 then provides the data to the multimodal analyzer316.

The structural analysis subsystem 310 uses the information from theultrasound transducer 120, in one embodiment, to generate one or morestructural measures. In other examples, these structural measures aregenerated by an OCT, sonar rangefinding, or other structural analysissubsystem 310. The structural analysis subsystem 310 produces structuralinformation, such as structural measures, which are alsospatially-resolved with respect to the vessels as the head 112 isscanned through the vessels 18. This structural information, such asstructural measures, is provided to the multi modal analyzer 316.

In more detail, the structural analysis subsystem 310 comprises thedrive electronics for driving the ultrasound transducer 120 andanalyzing the response of the transducer 120 to determine the structuralmeasure of interest in a IVUS-type system. In other examples, where thesecond energy source is an OCT system, the structural analysis subsystem310 is often an interferometer that resolves the phase or coherence ofthe light returning from the scanning catheter 112.

Generally, the analyzer 316 makes an assessment of the state of theblood vessel walls 104, which is presented to the operator via interface320. The collected spectral response is used to determine whether eachregion of interest of the blood vessel wall 104 comprises a lipid poolor lipid-rich atheroma, a disrupted plaque, a vulnerable plaque orthin-cap fibroatheroma (TCFA), a fibrotic lesion, a calcific lesion,and/or normal tissue.

In should be noted that the apparent separation between the structuralanalysis subsystem 310, chemical analysis subsystem 312, multimodalanalyzer 316, and the user interface 320 is provided to describe thevarious processing performed in the preferred embodiment and is thusonly a notional separation in some implementations. That is, the dataprocessing function of structural analysis subsystem 310, chemicalanalysis subsystem 312, multimodal analyzer 316 and the user interface320 are performed by one a single or one or more computer systems indifferent implementations.

The analyzer 316 uses the structural analysis information from thestructural analysis subsystem 310 to compensate information from thechemical analysis subsystem 312. Specifically, the structural analysissystem produces a structural measure that is used by the multimodeanalyzer 316. Examples of structural measures include the instantaneousdistance between the head of the catheter 112 and the blood vesselswalls 104 (D(wall)) and/or the thickness of the blood vessel walls.Another structural measure is the cap thickness (t_(c)) of the lesion102. This information is used to compensate information from thechemical analysis subsystem 312 such as serving as an input to achemometric algorithm that has dependencies on the instantaneous oraverage distance between the catheter head 112 and the blood vesselswalls 104. Still another structural measure is the lateral extents ofplaques in the blood vessel walls.

The pullback and rotation and rotation unit 105 is used both for themechanical drive to the scanning catheter 112 and also to couple theinformation or optical signals from both the IVUS and the NIR analysisportions of the catheter. Specifically, the pullback and rotation unit105 drives the scanning catheter 112 to rotate and withdraw through theouter sheath 114.

FIG. 3 is a flow diagram illustrating the operation of the multimodalanalyzer 316 in one embodiment.

Specifically, the NIR spectral response 410 is produced by the chemicalanalysis subsystem 312. Structural information 413 is further obtainedfrom the structural analysis sub system 310.

Depending on the implementation, the structural analysis information 413and the chemical analysis information 410 are produced during the sameor different scans of the scanning catheter 112. For example, in oneimplementation, the chemical analysis information 410 produced by theNIR analysis and structural information 413 produced by the IVUSanalysis are captured simultaneously while withdrawing and rotating thescanning catheter 112 through the blood vessels 104. In otherimplementations, the chemical analysis information 410 produced by theNIR analysis and structural information 413 produced by the IVUSanalysis are captured during different pullback and rotation operationsof the scanning catheter 112. Then the chemical analysis information 410data set produced by the NIR analysis and structural information 413data set are spatially aligned with respect to each other. Thisalignment includes compensation for the offset distance D(offset)between the IVUS transducer 120 and the optical bench 118, see FIG. 1.

This structural information is used in step 412 to determine whether ornot the instantaneous, i.e., spatially resolved, NIR spectral signal wasobtained from a distance of greater than 3 millimeters between the headof the scanning catheter 112 and the blood vessel wall 104.

If the distance was greater than 3 millimeters, then a real time updateis performed on preprocessing algorithms. In one example, suchpreprocessing algorithms are described in U.S. Patent Publication Numberis US 2004/0024298-A1, Publication Date Feb. 5, 2004, entitledSpectroscopic Unwanted Signal Filters for Discrimination of VulnerablePlaque and Method Therefor. This application is incorporated herein bythis reference in its entirety. Specifically, these preprocessingalgorithms process the near infrared information differently dependingupon the distance between the catheter head 112 and the blood vesselwall 104 when the information was obtained.

In step 416, a discrimination model is selected based upon the 0 to 2millimeters distance. The prior preprocessing step corrects datasetgenerated at greater than 3.0 mm such that they can not be analyzed witha discrimination model based on 0-2 mm distances.

In more detail, one of five thresholds 422, 426, 430, 434, 438 isapplied based upon a more the precise determination of the distancebetween the catheter head 112 and the blood vessel walls 104 produced bythe structural analysis 413. That is, for each location along the vesselwall, the corresponding NIR data are processes according to the distancebetween the catheter head 112 and the wall when the data were obtainedby reference to the structural analysis information 413. In theexamples, the granularity for the different thresholds is less than 0.5mm (step 420), 0.5-1.0 mm (step 424), 1.0-1.5 mm (step 428), 1.5-2.0 mm(step 432), and 2.0-2.5 mm (step 436). The data at each location alongthe wall is then processed using a separate one of the one of fivethresholds 422, 426, 430, 434, 438.

Thus, based upon the distance between the catheter head 112 and thevessel wall 104 when each NIR spectral signal is obtained, a differentthreshold is applied. The application of the threshold is used todetermine whether or not there is a high probability of a thin capatheroma or not, in one example in step 440.

FIG. 4 shows an alternative embodiment. This similarly usespreprocessing if the blood distance is greater than 3 millimeters instep 414. Then based upon the distance between the catheter head and thevessel walls when the data were obtained, different local models areapplied in steps 510, 512, 514, 516, 518. These are chemometric modelsthat are used to assess the NIR spectral signal 410.

Here, IVUS blood depth information is used to improve predictionaccuracy. Different chemometric prediction models 510, 512, 514, 516,518 are built for different blood depths: less than 0.5 mm (step 420),0.5-1.0 mm (step 424), 1.0-1.5 mm (step 428), 1.5-2.0 mm (step 432), and2.0-2.5 mm (step 436).

In some examples, the blood depths are determined “manually”. The userinputs the blood depth after measuring the IVUS image.

In other examples, NIR prediction models are augmented with the IVUSblood depth information.

FIG. 5 illustrates still another embodiment of the invention.Specifically, this illustrates that the point-by-point NIR analysis(Analysis (Pn)) of the blood vessels walls is compensated in each caseby the instantaneous information from the IVUS or first energy form(distance Pn). In this way, adjacent points in the scan of the innerwalls and their different NIR responses, (response of P1) and (responseof P2), are combined with the instantaneous distance to the vesselwalls, (distance P1) and (distance P2) when the NIR signal data 310 wasobtained to obtain distance compensated analyses Analysis (P1) andAnalysis (P2). In this way, the first energy form information is used ata very high level of granularity in order to compensate the NIR spectralsignal information at the spatial resolution of the chemical and/orstructural analysis modality.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1.-29. (canceled)
 30. A system for analyzing blood vessel walls, thesystem comprising: a catheter configured to be advanced through bloodvessels to a region of interest of the blood vessel wall; and acontroller coupled to the catheter and comprising; a structural analysissubsystem generating structural information at the region of interest ofthe blood vessel wall; a chemical analysis subsystem providing chemicalanalysis information of the region of interest of the blood vessel wall;and a multimodal analyzer configured to compensate the chemical analysisinformation from the chemical analysis subsystem based on the structuralinformation from the structural analysis subsystem to make an assessmentof the state of the blood vessel wall at the region of interest.
 31. Thesystem of claim 30, wherein the structural analysis subsystem comprisesan ultrasound transducer disposed within the catheter.
 32. The system ofclaim 30, wherein the structural information generated by the structuralanalysis subsystem comprises one or more of distance between thecatheter and the blood vessel wall at the region of interest, thicknessof the blood vessel wall at the region of interest, and cap thickness ofa lesion on the blood vessel wall.
 33. The system of claim 30, whereinthe chemical analysis subsystem comprises an optical bench disposedwithin the catheter for transmitting optical energy to the blood vesselwall and receiving optical energy reflected from the blood vessel wall.34. The system of claim 33 wherein the optical bench comprises: distalends of a delivery fiber and a collection fiber which extend betweenproximal and distal ends of the catheter; a delivery mirror configuredto redirect light emitted from the distal end of the delivery fibertowards the blood vessel wall, and a collection mirror configured toredirect light scattered from the blood vessel wall into the distal endof the collection fiber.
 35. The system of claim 30, wherein thechemical analysis subsystem analyzes the blood vessel walls bydetermining Raman spectral responses of the blood vessel wall fromdetected optical signals, by spatially resolving spectral responses ofthe blood vessel wall from detected optical signals, by determiningreflectance of the blood vessel wall from detected optical signals, orby determining fluorescence responses of the blood vessel wall fromdetected optical signals.
 36. The system of claim 30, wherein thechemical analysis subsystem analyzes the blood vessel walls by resolvingspectral responses of the blood vessel walls to generate spectral dataand using the spectral data to perform chemometric analysis of the bloodvessel walls.
 37. The system of claim 30, further comprising a pullbackand rotation system for simultaneously withdrawing the catheter throughthe blood vessels and rotating the catheter around its longitudinalaxis.
 38. The system of claim 30, wherein the multimodal analyzercompensates the chemical analysis information from the chemical analysissubsystem based on the structural information from the structuralanalysis subsystem by selecting a prediction model for analyzing thechemical analysis information based on the structural information or byselecting thresholds for analyzing the chemical analysis informationbased on the structural information.
 39. The system of claim 30, whereinthe structural analysis subsystem generates structural information byintravascular ultrasound, optical coherence tomography, opticalcoherence domain reflectometry, optical frequency domain imaging and/orsonar range finding.
 40. The system of claim 30, wherein the structuralanalysis subsystem generates structural information by intravascularultrasound using photoacoustically generated ultrasound from opticalenergy transmitted through the catheter.
 41. A system for processingdata signals from an intravascular catheter to analyze a blood vesselwall, the system comprising: a structural analysis subsystem receivingfirst signals from the catheter and generating structural informationrelating to the blood vessel wall; a chemical analysis subsystemreceiving second signals from the catheter and generating chemicalanalysis information relating to the blood vessel wall; and a multimodalanalyzer configured to compensate the chemical analysis information fromthe chemical analysis subsystem based on the structural information fromthe structural analysis subsystem to make an assessment of the state ofthe blood vessel wall.
 42. The system of claim 41, wherein thestructural analysis subsystem comprises drive electronics for driving anultrasound transducer in the catheter and analyzing a response of thetransducer to determine the structural information.
 43. The system ofclaim 41, wherein the structural analysis subsystem comprises aninterferometer that resolves the phase or coherence of light signalsreceived from the catheter.
 44. The system of claim 41, wherein thechemical analysis subsystem comprises a tunable laser coupled into anoptical fiber of the catheter.
 45. The system of claim 41, wherein thechemical analysis subsystem comprises one or multiple optical detectorsor spectrometers.
 46. The system of claim 41, wherein the structuralinformation generated by the structural analysis subsystem comprises oneor more of distance between the catheter and the blood vessel wall,thickness of the blood vessel wall, and cap thickness of a lesion on theblood vessel wall.
 47. The system of claim 41, wherein the secondsignals are optical signals and the chemical analysis subsystem analyzesthe blood vessel wall by determining Raman spectral responses of theblood vessel wall from the optical signals, by spatially resolvingspectral responses of the blood vessel wall from the optical signals, bydetermining reflectance of the blood vessel wall from the opticalsignals, or by determining fluorescence responses of the blood vesselwall from the optical signals.
 48. The system of claim 41, wherein thechemical analysis subsystem analyzes the blood vessel wall by resolvingspectral responses of the blood vessel wall to generate spectral dataand uses the spectral data to perform chemometric analysis of the bloodvessel walls.
 49. The system of claim 41, further comprising a pullbackand rotation system configured to be coupled to the catheter and tosimultaneously withdraw the catheter through the blood vessel and rotatethe catheter around its longitudinal axis.
 50. The system of claim 41,wherein the multimodal analyzer compensates the chemical analysisinformation from the chemical analysis subsystem based on the structuralinformation from the structural analysis subsystem by selecting aprediction model for analyzing the chemical analysis information basedon the structural information or by selecting thresholds for analyzingthe chemical analysis information based on the structural information.51. The system of claim 41, wherein the structural analysis subsystemgenerates structural information by intravascular ultrasound, opticalcoherence tomography, optical coherence domain reflectometry, opticalfrequency domain imaging, and/or sonar range finding.